Napolitano told reporters Monday in San Diego that the Border Patrol made about 463,000 arrests along the border during the federal government's fiscal year that ended Sept. 30. That's down from more than 556,000 the previous 12 months.

It marks the fifth straight year of declines.

Napolitano says the weak economy helps explain why fewer people are getting caught crossing the border illegally, and she also credits enforcement against employers. But she says a big reason is enforcement including more Border Patrol agents and 1,200 National Guard troops.